For which of the following reactions, the degree of dissociation (α) and equilibrium constant (KP) are related as

KP=4α2P/(1–α2)?

in the above reaction, the concentration of N2O4=1–α,

The concentration of NO2=α

Now, we know that mole fraction = number of moles/total miles

So, Kp= [(2α/1+α)p]2/[(1–α/1+α)p]

Kp=[(4α2)/(1+α)2P2]/[(1–α)/(1+α)P]

Kp=4α2p/1–α2

Therefore, the correct answer is option (A) N2O4(g)⇌2NO2(g).